GEOLOGY. 337 



B. — PALEOZOIC. 



8. Cambrian. — Lower and Middle Cambrian of Sedgwick ; Cambrian 

 and Primordial Silurian of Murchison, containing the first fauna of 

 Barrande. Embraces in iSTorth America tbe Menevian or Acadian, the 

 Potsdam and Calciferous divisions of the New York system, and the 

 Upper Taconic of Emmons or Quebec group of Logan. 



9. Ordovician or Ordovian. (Lapworth, 1879.) — Upper Cambrian of 

 Sedgwick; Lower Silurian of Murchison; Cambro-Silurian and Siluro- 

 Cambrian of others, containing the second fauna of Barrande. Em- 

 braces in North America the Chazy, Trenton, Utica, and Loraine divi- 

 sions of the New York system. 



10. Silurian. (Sedgwick) — Upper Silurian of Murchison, containing 

 the third fauna of Barrande. Includes in North America the Oneida, 

 Clinton, Niagara, and Lower Helderberg, of the New York system, w.ith 

 the intercalated Onondaga or Saliferous group. 



11. Devonian, or Erian of Dawson; the Erie division of the New York 

 system. - 



12. Carboniferous. 



PALEOZOIC ROCKS OF COLORADO. 



S. F. Emmons has given in the report of the United States geological 

 survey for 1881, an account of the geology of the Leadville district in 

 Colorado, where the Paleozoic rocks are associated with numerous erupt- 

 ive masses and contain large deposits of argentiferous lead-ores, which 

 have given to the region its economic importance. To the west of the 

 Front or Colorado Eange rises, with a gentle slope to the east, the Mus- 

 quito or Park Eange, attaining 11,000 feet, and sinking abruptly on 

 the west to the Arkansas Valley. This, which is sixty miles long and 

 fifteen miles wide, is limited to the west by the broad and lofty Sa- 

 watch Range. Within the valley, on the western flank of the Musquito 

 llange, is situated Leadville, 10,150 feet above the sea. We here find 

 reposing on the Eozoic rocks of the range a series of Paleozoic strata 

 consisting in ascending order (1) of 200 feet of strata, chiefly quartzites, 

 described as Cambrian ; (2) 200 feet of white doloraitic Silurian lime- 

 stone, to which succeed (3) about 4,000 feet of Carboniferous strata, 

 having at their base 200 feet of blue limestone, and at the summit from 

 1,000 to 1,500 feet, the Weber grits and shales intervening. The Kanab 

 section on the Colorado exhibits a similar thickness, a remarkable con- 

 trast with the Wahsatch in Utah, where King found a series of 30,000 

 feet of Paleozoic strata, including at the base 12,000 feet of sandstones 

 and shales, regarded as Cambrian, but without observed fossils save in a 

 few feet at the top, which carry a Potsdam fauna. The Mesozoic of the 

 Leadville region, which probably attained 1,000 feet, has been removed, 

 but the Paleozoic strata include eruptive rocks, mostly of the Mesozoic 

 period. These, which are described as quartziferous porphyries, some- 

 times granite-like, and diorites, are found in the Paleozoic series as inter- 

 H. Mis. 26 22 



